This invention relates to pattern cam selection devices for sewing machines of the type wherein the cam follower is moved toward or away from the cam for engagement or disengagement therewith.
These mechanisms typically utilize a movable bracket to which the cam follower is pivotally attached. The bracket is arranged so that the operator may effect movement thereof by manipulating a control mechanism. When engaging the follower, the bracket is moved so that the pivotal axis of the cam follower moves toward the pattern cam and causes one extremity of the follower to contact the cam surface and the other extremity to contact a connecting rod or bar associated with a stitch forming instrumentality of the sewing machine. Devices of this nature are disclosed in U.S. Pat. No. 3,332,380, Jul. 25, 1967, Keizo and U.S. Pat. No. 3,339,508, Sept. 5, 1967, Keizo, the teachings of which are incorporated herein by reference.
Other mechanisms utilize a movable surface which abuts a smoothly curved portion of the cam follower in such a way that the follower, when actuated by the cam, will rock on the movable surface, similar to the operation of a fulcrum. When disengaging the follower from the cam, the movable surface is simply moved away from the curved surface allowing a spring to retract the follower. An example of this construction is disclosed in U.S. Pat. No. 3,041,988, Jul. 3, 1962, Fujita, the teachings of which are incorporated herein by reference.
These constructions have the disadvantage that when moving the cam follower into engagement with a high lobe on the cam, the connecting rod or bar associated with a stitch forming instrumentality must be moved to its extreme position relative to the high lobe of the cam simultaneously with the follower being positioned into engagement with the cam. Therefore, in addition to the normal forces required for actuating the mechanism to engage the follower, there are the additional forces required to move the stitch forming instrumentality, such as a needle bar, to one of its extreme positions against a spring biasing force. These two forces when taken together can be significant and can render the manual actuation of such a cam selection device difficult.
A somewhat different construction utilizes a manually rotatable dial having two interrelated cam surfaces. As the dial is rotated, the first cam surface effects disengagment of the cam followers from the needle bar and feed control cams. Continuing rotation of the dial causes the second cam surface to effect indexing of the followers to the next cam position, whereupon the first cam surface effects engagement of the followers and newly selected cams. For each movement of the followers to a newly indexed position, the followers must first be retracted, indexed to the next position, then reengaged again. If it is desired to select a pattern cam which is several indexing positions away from the present follower position, the followers must be retracted and then reengaged for each position moved.
The present invention overcomes these disadvantages through the use of a novel but simple mechanism.